During cardiopulmonary bypass surgery, blood must be oxygenated and circulated artificially outside of the body. For external circulation to be successful, it is critical to provide a method for passive venous drainage and to prevent air bubbles from entering the bypass circuit. If an air bubble finds its way to the human brain, consequences include brain damage and death. The venous reservoir component of the cardiopulmonary bypass circuit provides passive drainage, but is especially susceptible to air bubble introduction. Two types of reservoir exist, the flexible reservoir and the hard-sided reservoir. A primed flexible reservoir is much less likely to introduce bubbles into the circuit than its counterpart, due to its ability to conform its shape to accommodate the volume of blood in the reservoir.
Currently, level detection is available for the hard-sided reservoir in the form of acoustic sensors that attach to the container. These sensors are capable of determining whether or not fluid has reached a certain level. Due to its nature, this detection mechanism is not capable of providing continuous volume data.
Level detectors have taken on many forms throughout their evolution. Capacitance, weight, and light-based systems are a few of the level detection methods that experienced limited success. However, these systems were plagued with issues, as in the weight-based system, where “the tragic defect in this device is that the device cannot differentiate between blood in the arterial reservoir and someone leaning on the weight arm. There have been reports of someone pushing down on the arm, the arterial pump head going to maximum RPM, and air being pumped into the patient.”
In terms of benefits, electronic level sensing relieves the perfusionist (the person in charge of the bypass circuit) of the extraneous duty of monitoring the venous reservoir. By eliminating a task for the perfusionist, this system will also reduce the likelihood of human error.